1. Field of the Invention
This invention relates to achieving more energy-efficient horizontal movement of a tree-working tool being carried on the end of a two-member knuckle boom. The term xe2x80x9ctree-working toolxe2x80x9d throughout this specification is intended to encompass, for example, saw heads and other devices (such as shear heads, for example), for cutting trees at the stump; tree delimbing heads; tree processing heads; wood-handling grapples for piling or loading trees or logs; and other such tools in the tree-harvesting industry.
FIGS. 1A and 1B show an example of such a two-member knuckle boom, used in the tree harvesting industry for tree felling with a disc saw. It must often move a tree-harvesting implement in and out about 12 feet while not changing its height above the ground. It comprises a xe2x80x9choist boomxe2x80x9d having a proximal end pivoted to the machine base, and a xe2x80x9cstick boomxe2x80x9d having a proximal end pivoted to the distal end of the hoist boom. The disc saw is mounted on the distal end of the stick boom.
A particular concern in the tree harvesting industry, but in other industries as well, is the large amount of diesel fuel that is consumed when felling or delimbing or otherwise processing trees using tools carried by such knuckle booms.
Another concern in the industry is to improve the machine operator""s ability to achieve near horizontal tool travel at a controlled velocity, as easily as possible. As noted in the present inventor""s U.S. Pat. No. 5,794,674, it is a burden on saw designers to provide saws that are light enough for long reaches yet durable enough to withstand the often errant feed of two-lever manual control. This invention provides control of horizontal tool motion with a single control movement, such as forward and back movement of a hand lever.
2. Description of the Prior Art
Most logging machine reaching is done with knuckle booms that retain the energy-wasteful reaching characteristics of digging and load lifting machines, from which they were originally adapted. There is concern about the amount of hydraulic oil heat generated, and corresponding fuel consumed, that result when the tool, with or without a load, is moved horizontally with the knuckle boom, towards and away from the machine.
Some other prior art machinery uses sliding (or telescopic) booms to get energy-efficient linear movement and ease of operation on xe2x80x9creaching boomxe2x80x9d applications, but these present major problems in design for reliabilityxe2x80x94for example in the hose runs to feed the implement being carried out on the end, and in providing wear surfaces or rollers and raceways to accommodate continuous sliding action in adverse conditions. U.S. Pat. No. 3,981,336 (Levesque) shows a felling and delimbing device that was intended to telescope horizontally. U.S. Pat. No. 4,276,918 (Sigouin) and U.S. Pat. No. 4,428,407 (Bourbeau) are examples of telescopic and horizontally sliding delimbers that have proven to be difficult to maintain.
Still others have chosen to ease operator requirements and reduce reach energy losses by designing their booms with built-in parallelograms, but the additional links, pins and levers needed to achieve the desired boom end coverage geometry add much to machine weight and promise poor reliability when used in adverse logging conditions. U.S. Pat. No. 5,170,825 (Elliot) shows one such linkage boom and describes well the recently evolving needs to support and move a disc saw felling head along a suitable path. Other earlier linkage type booms that had not anticipated disc saw felling and boom delimbing are represented by illustrations in U.S. Pat. No. 3,590,760 (Boyd). The present inventor""s U.S. Pat. No. 4,446,897 is an example of side-cut (swing-cut) being substituted for a preferred but uncertain reach-cut.
On knuckle boom machines the diesel engine power used for horizontal reaching can be measured from determining the amount of hydraulic oil pumped and its pressure, and then adding a small amount for friction losses.
To help visualize the wastefulness of a prior art boom during a full reach action, it should be noted that when horizontal reach action is being achieved by simultaneously supplying oil to both the hoist and stick cylinders in the right proportions, the amount of oil needed and its pressures are nearly the same as if the load (boom members, tool and tree) was sequentially first fully lifted by one cylinder and then lowered by the other. For example, to extend a disc saw or other tool out horizontally, hydraulic oil being pumped from the reservoir at a working pressure is directed by a stick valve to the base of a stick cylinder while a hoist directional-control valve drains already pumped oil from the base end of the hoist cylinder to the reservoir. The stick valve also drains oil from the stick cylinder rod-end to the reservoir; and the hoist valve also sends pumped oil from the reservoir to the hoist cylinder rod end. In other words, on prior art knuckle boom machines, near-horizontal travel paths for the end point of a knuckle boom are now typically achieved by simultaneously feeding to and removing the correct amount of hydraulic oil from hydraulic cylinders. A definite amount of oil heat is generated, and is readily calculable by those knowledgeable in the field of the invention. When closely examined it can be seen that such oil flows are very inefficient and require installation of high horsepower diesel engines and large cooling systems, causing high fuel consumption.
It is an object of this invention to avoid excessive hydraulic oil heat generation and excessive fuel consumption during reaching in and out, and to do this without significantly changing the hydraulic pump and valve systems of the carrier machines, nor departing from the structural compactness of the prior art knuckle booms.
Another object of the preferred embodiment of the invention is to provide for easier operation and training, by allowing a beginner operator to achieve horizontal tool path travel using only one control motion, for example a back and forth hand control lever, resulting in a much shorter learning time than with the two levers of the prior art. The operator""s other hand is thus freed for controlling the tilt of the tool.
In the invention, therefore, hydraulic line connections are arranged so that simultaneous supply and dumping of load-supporting pressurized oil during reaching is avoided, so that engine power is needed primarily for friction and flow losses.
This invention therefore shunts pressurized oil directly from the collapsing hoist cylinder base-end to the extending cylinder base-end, where it continues to do useful load support work and thereby avoids most of the problematic heat generation.
This invention separates out the load-carrying work from the reach positioning function of the knuckle boom and leaves that load-carrying work with the hoist and stick cylinders. A separate xe2x80x9creachxe2x80x9d cylinder is introduced, which does not carry load but instead controls the reach action. Because in good knuckle boom designs the hoist and stick cylinders have always carried their loads at nearly equal pressures, although on separate circuits, it is possible to connect their base ends together with a hydraulic line so that a load-supporting pressurized volume or xe2x80x9cslugxe2x80x9d of oil can flow between them, while the reach cylinder alters the knuckle angle to get reach action. The reach cylinder also provides the make-up force which is needed to stabilize the knuckle boom, since the hoist and stick cylinders operate at exactly the same oil pressure.
Although in theory the reach cylinder needs to be only large enough to overcome all the frictions and to make up any mismatching between the hoist and stick cylinders, in practice it preferably is sized to be robust like the other cylinders, so that it is not easily damaged and so that it can be used to do push and pull work if desired. The oil that this cylinder receives from the pump and dumps to the reservoir is not as wasteful as the hoist and stick oil of the prior art. That is because its pressure for unloaded reach is not far from the theoretical zero, and when useful reach work is being done, such as pushing or pulling a saw head, that is where the energy goes, i.e. into external work done, not into oil heat.
Ideally, the cylinder sizing and pinning geometry can be designed so that the volume of hydraulic oil in the stick cylinder base, added to that in the hoist cylinder base, is approximately constant as the stick boom point moves on a horizontal path. When this is done, energy saving is maximized and a single-action control gives horizontal tool travel. A slight departure from this rule will not result in a failure of this invention, but will result in a corresponding slight reduction in energy savings, and will require some use of a second control action to get more exact horizontal tool travel, if needed.